With such actuating drives the element to be positioned is mounted on a one or more axis gimbal system. Each of the individual axes is provided with an actuating drive. The actuating drive comprises a torque motor and an angle pick-off. The torque motor is energized through an electronic control device. A desired value signal is supplied to the electronic control device. This desired value signal determines the position which the element is to adopt. The torque motor rotates the element to be positioned such that the angle pick-off provides a feedback signal corresponding to the desired position.
Often rather large torques have to be exerted for this positioning movement. These torques occur, for example, when a robot arm has to lift or even to hold a load. Torques have also to be overcome during the positioning movement due to moments of inertia of the moving parts.
Actuating drives exist wherein the rotary element, which is to be positioned, is connected directly with the rotor of the torque motor. This permits very accurate positioning. The positioning accuracy is determined substantially only by the quality of the angle pick-up.
In order to exert large torques, however, a large torque motor is required with such actuating drives, which is fed by a high power current. Such torquers increase the volume of the device. Due to the mass and the moment of inertia of the torque motor, a higher torque for positioning is required.
A further problem, which arises in particular during continuous operation, is the heating up of the system due to the current supplied to the torque motor. Such heating up or quick temperature changes counteract the requirement of high positioning accuracy.
Actuating drives are also known, wherein the torque motor is connected with the rotary element through a step down system. Thereby smaller torque motors can be used. In addition, operation with lower currents is possible. However the accuracy of the positioning is reduced due to friction and play in the step down system.